Allergic Reaction

Topic Overview

Allergies are an overreaction of the body's natural defense system that helps fight infections (immune system). The immune system normally protects the body from viruses and bacteria by producing antibodies to fight them. In an allergic reaction, the immune system starts fighting substances that are usually harmless (such as dust mites, pollen, or a medicine) as though these substances were trying to attack the body. This overreaction can cause a rash, itchy eyes, a runny nose, trouble breathing, nausea, and diarrhea.

An allergic reaction may not occur the first time you are exposed to an allergy-producing substance (allergen). For example, the first time you are stung by a bee, you may have only pain and redness from the sting. If you are stung again, you may have hives or trouble breathing. This is caused by the response of the immune system.

Many people will have some problem with allergies or allergic reactions at some point in their lives. Allergic reactions can range from mild and annoying to sudden and life-threatening. Most allergic reactions are mild, and home treatment can relieve many of the symptoms. An allergic reaction is more serious when severe allergic reaction (anaphylaxis) occurs, when allergies cause other problems (such as nosebleeds, ear problems, wheezing, or coughing), or when home treatment doesn't help.

Allergies often occur along with other diseases, such as asthma, ear infections, sinusitis, and sleep apnea. For more information, see the topic Allergic Rhinitis.

Types of allergies

There are many types of allergies. Some of the more common ones include:

  • Food allergies, which are more common in children than adults. Food allergies are most common in people who have an inherited tendency to develop allergic conditions. These people are more likely to have asthma and other allergies. For more information, see the topic Food Allergies.
  • Medicine allergies. Many prescription and nonprescription medicines can cause an allergic reaction. Allergic reactions are common and unpredictable. The seriousness of the allergic reaction caused by a certain medicine will vary.
  • Allergies to insect venom. When you are stung by an insect, poisons and other toxins in the insect's venom enter your skin. It is normal to have some swelling, redness, pain, and itching at the site of a sting. An allergic reaction to the sting occurs when your body's immune system overreacts to the venom of stinging insects. For more information, see the topic Allergies to Insect Stings.
  • Allergies to animals, which are more likely to cause breathing problems than skin problems. You may be allergic to your pet's dead skin (dander), urine, dried saliva, or hair.
  • Allergies to natural rubber (latex). Some people develop allergic reactions after repeated contact with latex, especially latex gloves.
  • Allergies that develop from exposure to a particular inhaled substance in the workplace. These are called occupational asthma.
  • Allergies to cosmetics, such as artificial nails, hair extensions, and henna tattoos.

Seasonal allergies show up at the same time of the year every year and are caused by exposure to pollens from trees, grasses, or weeds. Hay fever is the most common seasonal allergy.

Allergies that occur for more than 9 months out of the year are called perennial allergies.

Year-round symptoms (chronic allergies) are most likely to occur from exposure to animal dander, house dust, or mold.

Check your symptoms to decide if and when you should see a doctor.

Health Tools Health Tools help you make wise health decisions or take action to improve your health.

Health Tools help you make wise health decisions or take action to improve your health.


Decision Points focus on key medical care decisions that are important to many health problems. Decision Points focus on key medical care decisions that are important to many health problems.
  Allergies: Should I Take Allergy Shots?
  Allergies: Should I Take Shots for Insect Sting Allergies?
Actionsets help people take an active role in managing a health condition. Actionsets are designed to help people take an active role in managing a health condition.
  Allergies in Children: Giving an Epinephrine Shot to a Child
  Allergies: Giving Yourself an Epinephrine Shot

Check Your Symptoms

Are you concerned about an allergic reaction?
Yes
Allergic reaction concerns
No
Allergic reaction concerns
How old are you?
Less than 12 years
Less than 12 years
12 years or older
12 years or older
Are you male or female?
Male
Male
Female
Female
Could you be having a severe allergic reaction?
This is more likely if you have had a bad reaction to something in the past.
Yes
Possible severe allergic reaction (anaphylaxis)
No
Possible severe allergic reaction (anaphylaxis)
Do you have symptoms of shock?
Yes
Symptoms of shock
No
Symptoms of shock
Have you ever had a severe allergic reaction?
A severe allergic reaction affects the whole body. Your doctor may have called it anaphylaxis.
Yes
History of severe allergic reaction
No
History of severe allergic reaction
Have you been exposed to the same thing (or something similar to it) that caused a severe reaction in the past?
For example, this could be an insect, a certain food, or a type of medicine or drug.
Yes
Reexposed to substance that caused past severe reaction
No
No new exposure to substance that caused past severe reaction
Not sure
Possibly reexposed to substance that caused past severe reaction
Are you having any symptoms of an allergic reaction now, even mild ones?
If you've ever had a severe reaction to the same thing that's causing your symptoms now, treat this as an emergency. Mild symptoms quickly may become severe.
Yes
History of severe reaction with symptoms now
No
History of severe reaction with symptoms now
Are you having trouble breathing (more than a stuffy nose)?
Yes
Difficulty breathing more than a stuffy nose
No
Difficulty breathing more than a stuffy nose
Is there any new swelling?
Yes
New swelling
No
New swelling
Are the lips, tongue, mouth, or throat swollen?
Yes
Swelling of lips, tongue, mouth, or throat
No
Swelling of lips, tongue, mouth, or throat
Did the lips, tongue, mouth, or throat swell quickly?
Yes
Rapid swelling of lips, tongue, mouth, or throat
No
Rapid swelling of lips, tongue, mouth, or throat
Does swelling involve the palms of the hands, the soles of the feet, or the area from one large joint to another, such as from the ankle to the knee?
Yes
Swelling is across two joints, on soles of feet, or on palms of hands
No
Swelling is across two joints, on soles of feet, or on palms of hands
Is the swelling quickly getting worse (over hours or days)?
Yes
Swelling is quickly getting worse
No
Swelling is quickly getting worse
Did you get an epinephrine shot, either on purpose (to treat the reaction) or by accident?
Yes
Has had epinephrine shot
No
Has had epinephrine shot
Is most of your body covered in hives?
Hives are raised, red, itchy patches of skin. They usually have red borders and pale centers. They may seem to move from place to place on the skin.
Yes
Hives covering most of body
No
Hives covering most of body
Did the hives appear within the past 3 hours?
Yes
Hives appeared within past 3 hours
No
Hives appeared within past 3 hours
Are there any symptoms of infection?
Yes
Symptoms of infection
No
Symptoms of infection
Do you think you may have a fever?
Yes
Possible fever
No
Possible fever
Are there red streaks leading away from the area or pus draining from it?
Yes
Red streaks or pus
No
Red streaks or pus
Do you have diabetes, a weakened immune system, peripheral arterial disease, or any surgical hardware in the area?
"Hardware" includes things like artificial joints, plates or screws, catheters, and medicine pumps.
Yes
Diabetes, immune problems, peripheral arterial disease, or surgical hardware in affected area
No
Diabetes, immune problems, peripheral arterial disease, or surgical hardware in affected area
Does your skin itch?
Yes
Itchy skin
No
Itchy skin
Is the itching severe?
Severe means that you are scratching so hard that your skin is cut or bleeding.
Yes
Severe itching
No
Severe itching
Has the itching interfered with sleeping or normal activities for more than 2 days?
Yes
Itching has disrupted sleep or normal activities for more than 2 days
No
Itching has disrupted sleep or normal activities for more than 2 days
Could you be having an allergic reaction to a medicine?
Almost any medicine can cause an allergic reaction. Think about whether the problem started soon after you began using a new medicine or a higher dose of a medicine.
Yes
Medicine may be causing allergic reaction
No
Medicine may be causing allergic reaction
Have your symptoms lasted longer than 2 weeks?
Yes
Symptoms for more than 2 weeks
No
Symptoms for more than 2 weeks

Many things can affect how your body responds to a symptom and what kind of care you may need. These include:

  • Your age. Babies and older adults tend to get sicker quicker.
  • Your overall health. If you have a condition such as diabetes, HIV, cancer, or heart disease, you may need to pay closer attention to certain symptoms and seek care sooner.
  • Medicines you take. Certain medicines, herbal remedies, and supplements can cause symptoms or make them worse.
  • Recent health events, such as surgery or injury. These kinds of events can cause symptoms afterwards or make them more serious.
  • Your health habits and lifestyle, such as eating and exercise habits, smoking, alcohol or drug use, sexual history, and travel.

Symptoms of difficulty breathing can range from mild to severe. For example:

  • You may feel a little out of breath but still be able to talk (mild difficulty breathing), or you may be so out of breath that you cannot talk at all (severe difficulty breathing).
  • It may be getting hard to breathe with activity (mild difficulty breathing), or you may have to work very hard to breathe even when you’re at rest (severe difficulty breathing).

Call 911 Now

Based on your answers, you need emergency care.

Call911or other emergency services now.

If you have an emergency allergy kit that contains an epinephrine shot, use it while you wait for help to arrive. Follow the directions on the label about how to give the shot.

Shock is a life-threatening condition that may quickly occur after a sudden illness or injury.

Symptoms of shock (most of which will be present) include:

  • Passing out.
  • Feeling very dizzy or lightheaded, like you may pass out.
  • Feeling very weak or having trouble standing.
  • Not feeling alert or able to think clearly. You may be confused, restless, fearful, or unable to respond to questions.

Symptoms of infection may include:

  • Increased pain, swelling, warmth, or redness in or around the area.
  • Red streaks leading from the area.
  • Pus draining from the area.
  • A fever.

Symptoms of a severe allergic reaction (anaphylaxis) may include:

  • The sudden appearance of raised, red areas (hives) all over the body.
  • Rapid swelling of the throat, mouth, or tongue.
  • Trouble breathing.

A severe reaction can be life-threatening. If you have had a bad allergic reaction to a substance before and are exposed to it again, treat any symptoms as an emergency. Even if the symptoms are mild at first, they may quickly become very severe.

Certain health conditions and medicines weaken the immune system's ability to fight off infection and illness. Some examples in adults are:

  • Diseases such as diabetes, cancer, heart disease, and HIV/AIDS.
  • Long-term alcohol and drug problems.
  • Steroid medicines, which may be used to treat a variety of conditions.
  • Chemotherapy and radiation therapy for cancer.
  • Other medicines used to treat autoimmune disease.
  • Medicines taken after organ transplant.
  • Not having a spleen.

Seek Care Now

Based on your answers, you may need care right away. The problem is likely to get worse without medical care.

  • Call your doctor now to discuss the symptoms and arrange for care.
  • If you cannot reach your doctor or you don't have one, seek care in the next hour.
  • You do not need to call an ambulance unless:
    • You cannot travel safely either by driving yourself or by having someone else drive you.
    • You are in an area where heavy traffic or other problems may slow you down.

Shock is a life-threatening condition that may occur quickly after a sudden illness or injury.

Symptoms of shock in a child may include:

  • Passing out.
  • Being very sleepy or hard to wake up.
  • Not responding when being touched or talked to.
  • Breathing much faster than usual.
  • Acting confused. The child may not know where he or she is.

Try Home Treatment

You have answered all the questions. Based on your answers, you may be able to take care of this problem at home.

  • Try home treatment to relieve the symptoms.
  • Call your doctor if symptoms get worse or you have any concerns (for example, if symptoms are not getting better as you would expect). You may need care sooner.

Seek Care Now

Based on your answers, you may need care right away. The problem is likely to get worse without medical care.

  • Call your doctor now to discuss the symptoms and arrange for care.
  • If you cannot reach your doctor or you don't have one, go to the emergency room now. You may have a reaction after the epinephrine wears off.
  • You do not need to call an ambulance unless:
    • You cannot travel safely either by driving yourself or by having someone else drive you.
    • You are in an area where heavy traffic or other problems may slow you down.

Seek Care Today

Based on your answers, you may need care soon. The problem probably will not get better without medical care.

  • Call your doctor today to discuss the symptoms and arrange for care.
  • If you cannot reach your doctor or you don't have one, seek care today.
  • If it is evening, watch the symptoms and seek care in the morning.
  • If the symptoms get worse, seek care sooner.

Make an Appointment

Based on your answers, the problem may not improve without medical care.

  • Make an appointment to see your doctor in the next 1 to 2 weeks.
  • If appropriate, try home treatment while you are waiting for the appointment.
  • If symptoms get worse or you have any concerns, call your doctor. You may need care sooner.

Home Treatment

You can use home treatment to relieve symptoms of:

  • Itching or hives. Avoid more contact with whatever you think is causing the hives.
  • A sore throat caused by postnasal drip. People age 8 years or older can gargle with warm salt water at least once each hour to help ease throat soreness.
  • Hay fever. Take an antihistamine to reduce symptoms of itchy, watery eyes; sneezing; or a runny, itchy nose. Be sure to read and follow any warnings on the label. Don't give antihistamines to your child unless you've checked with the doctor first.
  • Allergies that are worse in damp weather. Mold may be the cause of allergies that get worse in damp weather. Mold produces spores that move, like pollen, in outdoor air during warmer months. During winter months, indoor molds can also be a problem.
  • Indoor allergies. Newer, energy-saving homes that are built with double- or triple-paned windows and more insulation keep heat and allergens indoors.
  • Allergies to a pet or other animal. When allergies are worse around pets, symptoms may be caused by your pet's dead skin (dander), urine, dried saliva, or hair.
  • Seasonal allergies. These are often caused by exposure to pollen.

For tips on how to treat dry and irritated skin, see the topic Dry Skin and Itching.

For information on how to treat an insect bite or sting, see the topic Insect Bites and Stings and Spider Bites.

Symptoms to watch for during home treatment

Call your doctor if any of the following occur during home treatment:

  • Trouble breathing, wheezing, or tightness in the chest develops.
  • Swelling of the throat, tongue, lips, or mouth develops.
  • Hives develop or get worse.
  • Swelling gets worse.
  • A skin infection develops.
  • Symptoms have not improved after 2 weeks of home treatment.
  • Symptoms become more severe or more frequent.

Prevention

To prevent problems with severe allergic reactions:

To prevent seasonal or year-round allergy reactions:

  • Control exposure to outdoor allergens. Limit the time you spend outside during allergy season. This may be the best approach to controlling your symptoms. If you have a seasonal allergy:
    • During the peak of the pollen or mold season, consider taking your vacation in a place that has fewer of these substances.
    • Exercise regularly. Exercise produces adrenaline, a natural way to relieve a stuffy nose. But exercising outdoors may also expose you to more pollen or mold spores.
  • Control exposure to indoor allergens. Newer, energy-saving homes built with double- or triple-paned windows and more insulation keep allergens and heat indoors.
    • Use an air conditioner or air purifier with a high-efficiency particulate air (HEPA) filter.
    • Keep the house aired out and dry. Keep the moisture level below 50%. Use a dehumidifier during humid weather.
    • Dust and vacuum 1 to 2 times a week. Use a vacuum cleaner with a HEPA filter, which collects dust-mite particles and pollen. Standard paper bag filters may allow the stirred-up allergens to escape back into the room.
    • Avoid carpet, upholstered furniture, and heavy drapes that collect dust. Vacuuming doesn't pick up dust mites. Remove rugs and wall-to-wall carpeting. Talk with your family about this measure and how this will affect family life. Replace drapes and blinds with roll-down shades or washable curtains.
    • Damp mop the floor once a day. Vacuum the walls, ceiling, closet, and the backs of the furniture once a week to get rid of as much dust as you can.
    • Use baking soda, mineral oil, club soda, or vinegar to clean instead of using harsher cleaning solutions that can produce allergic reactions.
    • Contact a pest control service, if necessary, to get rid of cockroaches. Cockroaches and dead insects may provoke allergic responses if you have allergic asthma.
    • Avoid tobacco smoke, smoke from wood-burning stoves, and fumes from kerosene heaters.
    • Keep air registers closed if there is a pet in the house. This will reduce the amount of animal dander circulating in the house, especially in the bedroom.
    • Repair any water-damaged areas from leaking roofs or basements. These areas can be prime mold-growing areas.
  • Control exposure to animal dander (dead skin or scales from animals). Indoor pets can spread dander and other pet-related allergens such as urine and dried saliva throughout your home. Cats in particular spread dried saliva, but other small animals such as mice and gerbils can spread it too. Hair is often not the problem. Short-haired animals are no less of a problem than long-haired ones.
    • Keep the pet outside of the house or at least out of the bedroom.
    • Bathe your pet once a week.
    • Ask a family member who does not have allergies to clean your pet's litter box.
    • Keep a caged pet, such as a gerbil, outside your home in a garage or shed.
    • Consider finding your pet a new home if your symptoms are severe.
  • Be sure to tell your child's school staff about his or her allergies. This is important so the school knows how to help your child if he or she has an allergic reaction.

Breast-feeding may prevent allergies. Breast-feed your baby for at least 6 months if possible to boost his or her immune system. Feeding only breast milk during the first 6 months of life may reduce the chances that your child will develop food allergies or may decrease the severity of your child's allergies. For more information, see the topic Breast-Feeding.

Preparing For Your Appointment

To prepare for your appointment, see the topic Making the Most of Your Appointment.

You can help your doctor diagnose and treat your condition by being prepared to answer the following questions:

  • What are your allergy symptoms?
  • How long have you had these symptoms?
  • Do you have an idea of what is causing your symptoms?
  • Are your allergies present all year, or do they get better or worse with different seasons?
  • What have you tried at home to decrease your symptoms? Has it helped?
  • What prescription or nonprescription medicines have you tried in the past? What worked and what didn't?
  • What other prescription and nonprescription medicines are you taking?
  • Have you recently gotten a tattoo or body piercing?
  • Do you have any health risks?

Credits

By Healthwise Staff
William H. Blahd, Jr., MD, FACEP - Emergency Medicine
H. Michael O'Connor, MD - Emergency Medicine
Last Revised November 11, 2013

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